The present invention relates to microlenses, and more particularly, to liquid microlenses.
Optical components are widely used in many optoelectronic applications that require light to be focused onto a specific point. Such applications include optical telecommunications applications and applications that simulate the function of the human eye. Traditionally in such applications, manual positioning and tuning of a lens and its surrounding support structure is required to maintain focus of the image onto a detector and to receive light beams originating from different angular directions relative to the lens. However, devices that rely on such manual positioning can be slow and quite expensive.
In one attempt to eliminate this manual tuning, small tunable lenses (also known as tunable microlenses) were developed to achieve optimal optical coupling between an optical source and an optical signal receiver, such as a photodetector. The microlens acts to focus the optical signal onto its intended destination (e.g., the photodetector). In some cases the refraction index of these microlenses is automatically varied in order to change the focus characteristics of the microlens when the incidence of a light beam upon the microlens varies from its nominal, aligned incidence. Thus, the desired coupling is maintained between the microlens and the photodetector. Therefore, the manual positioning and adjustment required in previous systems is eliminated.
Most tunable microlenses are either gradient index (GRIN) lenses with the refractive index controlled electrostatically or flexible polymeric lenses with the shape (and, therefore, the focal length) controlled mechanically. Both technologies have inherent limitations that impose severe restrictions on the performance of these existing tunable microlenses.
Tunable gradient index lenses have inherent limitations associated with the relatively small electro-optic coefficients found in the majority of electro-optic materials. This results in a small optical path modulation and, therefore, requires thick lenses or very high voltages to be employed. In addition, many electro-optic materials show strong birefringence that causes polarization dependence of the microlens, which distorts light with certain polarizations.
Mechanically adjustable flexible lenses typically have a substantially wider range of tunability than the gradient index lenses. However, they require external actuation devices, such as micropumps, to operate. Integration of such actuation devices into optoelectronic packages involves substantial problems associated with their miniaturization and positioning. These become especially severe in the case where a two-dimensional array of tunable microlenses is required.
Attempts have also been made to use other technologies to produce tunable microlenses, such as liquid microlenses controlled through self-assembled monolayers. Some of these attempts are described in U.S. Pat. No. 6,014,259, issued Jan. 11, 2000, the entirety of which is hereby incorporated by reference herein. Microlenses utilizing self-assembled monolayers, however, also suffer from several problems, including severe limitations on material selection and strong hysteresis often leading to the failure of the microlens to return to an original shape after a tuning voltage is disconnected.
More recent attempts have involved developing liquid microlenses that permit lens position and focal length adjustments. Examples of such microlenses, which utilize electrowetting principles coupled with external electronic control systems to accomplish these position and focal length adjustments, are described in copending U.S. patent applications Ser. No. 09/884,605, filed Jun. 19, 2001, entitled xe2x80x9cTunable Liquid Microlensxe2x80x9d and Ser. No. 09/951,637, filed Sep. 13, 2001, entitled xe2x80x9cTunable Liquid Microlens With Lubrication Assisted Electrowetting.xe2x80x9d The alignment and calibration of such microlenses is the subject of copending U.S. patent applications Ser. No. 10/135,973, filed Apr. 30, 2002, entitled xe2x80x9cMethod And Apparatus For Aligning A Photo-Tunable Microlensxe2x80x9d and Ser. No. 10/139,124, filed May 3, 2002, entitled xe2x80x9cMethod And Apparatus For Calibrating A Tunable Microlens,xe2x80x9d respectively. The ""605, ""637, ""973 and ""124 applications are hereby incorporated by reference herein in their entirety.
We have recognized that none of the above-described microlenses, allow for changing the directional view of the lens without manual repositioning of the structure upon which the lens is disposed. Additionally, the field of view of prior microlenses is strictly limited by the size and shape of the microlens. Therefore, while the aforementioned applications provide exemplary electrowetting-based tunable liquid microlenses, we have recognized that there remains a need to provide a tunable liquid microlens that does not require manual repositioning of the structure underlying the lens to change the directional view and the field of view of the lens. In particular, in certain applications it may be advantageous to have a microlens that is able to achieve a new directional view and have an increased field of view without such manual repositioning.
Therefore, we have invented a microlens that uses a substrate having a non-zero radius of curvature. Illustratively, the directional view of the microlens is altered by passing a current over at least one of a plurality of electrodes and thereby causing a voltage differential between the at least one of a plurality of electrodes and a conducting droplet of liquid disposed on the substrate with a non-zero radius of curvature. As the droplet moves to a different point along the surface of the substrate having a non-zero radius of curvature, the directional view the microlens changes in a way such that light originating from the new directional view is more advantageously focused into an image on a detector. The field of view of the microlens, therefore, is only limited by the area over which the liquid droplet can move.